Note: Descriptions are shown in the official language in which they were submitted.
1~8~3
The present invention relates to a process for improv-
ing the enzymatic softening of furs by using a special protease
effective in the acid pH range.
The drying of skins and hides constitutes a fundamental
change in the water balance of the proteins which participate
in the building-up of the skin. In particular, the protein
materials which are located between the collagen fibers and
which are water soluble in the natural state, but which are
less responsible for the skin structure, are denatured, whereby
the collagenous bundles of fibers, responsible for the elasti-
city and strength of the skin, stick together (agglutinate~ and
harden. The absorption of water is thereby greatly obstructed
after dehydration of the skins.
It is known to soften hides and skins enzymatically
in the neutral and slightly alkaline pH ranges by means of
enzymatic agents, with and without an additive of wetting agents.
The non-structured protein materials which cause the skin fiber
network to agglutinate and obstructlthe softening process, are
decomposed and dissolved out. In this manner, the softening
and returning of the hides and skins to the natural swollen
state by absorption of water are considerably accel~rated.
Processes for the enzymatic softening of furs which
are performed by using proteolyti enzymes, have already been
described in German Patent Specifications Nos. 847,947, 941,680,
972,832, and 976,602.
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o
However, all the proteases used in these processes
have the disadvantage that either the pickling or softening
effect is inadequate, or a certain amount of loosening of the
hair has to be accepted. Thus, the above-mentioned patent
specifications recommend working at acid p~I values, or the
~oint use of carbohydrases, although this does not achieve the
object in a really satisfactory manner. For this reason,
German Offenlegungsschrift 16 69 353 describes a process for
loosening the fibrous structure of furs in which the enzyme
takes effect only after the tanning agent takes effect.
In accordance with German Patent Specification No.
18 00 891, the same enzymes are used for softening as are used
for depilation, the enzyme concentrations being, of course,
reduced by the factor 10 in the former field of application
and the pH value being adjusted to 3 to 4. It is obvious that,
under these conditions, either the risk of loss of the hair
has to be accepted ~r an optimum softening effect has to be
foregone.
According to the present invention, the satisfactory
softening of furs, or fur skins, particularly high-grade furs
such as mink or Persian lamb, may be achieved while at the
same time taking the greatest possible care of the appearance
of the hair. The present invention is directed to a process
for the enzymatic softening of furs, which comprises contacting
a fur with an acid aqueous liquor containing an acid protease
from a fungus strain of the genus Rhizopus rhizopodiformis
... . . ~ _, . ~ .. , . ~ _, _, .. _ .. _ _ ~ _ _, , . _ , . .. .. _ . _ _ . _ .. , . .. , . _ _ _ _ . _ _ _
(as hereinafter identified), said acid protease being effective
in the pH range of from about 2.5 to 6.5.
The softening of the furs may also comprise contacting
the fur with wetting agents and/or inorganic salts.
The acid protease from a fungus strain of the genus
Rhizopus rhizopodiformis which is used in the process of the
present invention has been filed at the Central Bureau voor
Schimmelcult~ s, Baarn, Holland, and has been given the
filing number CBS 227.75.
In accordance with U. S. Pat. No. 4,062,732, ~e~r~
-hePe~by rcf~P~the protease used having the Filing Number CBS 227.75
(Central Bureau ~oor Schimmelcultures, Baarn, Holland), is
obtained by the anaerobic culture of a fungus strain of the
genus Rhizopus rhizopodiformis in a nutrient, which contains
assimilable carbon and nitrogen sources, at pH values between
3 and 7 and temperatures between 25 and 50C, and~ in a known
manner, separating out the enzyme produced. The enzyme has a
wide spectrum of activity in the slightly acid pH range of
from about 2.5 to 6.5, with an optimum acti~ity at the pH range
of from about 4.5 to 5. 2.
The proteolytic activity of the present protease is
determinea by the known Anson principle, whereby a suitably
diluted quantity of enzyme solution is incubated for twenty
minutes at 40C with an equal volume of 1.2% casein solution,
the latter containing 0. 6% of lactic acid, 6 mol of urea3
and 0.1 mol of citric or acetic acid. The pH ~alue of the
casein solution is adjusted to 4.5 by adding 2 N caustic soda
solution. After incubation, 0. 4 N trichloroacetic acid is
_ .. .. ~ .. .. --.. ~.. ,,~_"___. , ._. _ ........ ,, ._.. ._~ _ . _.. ___.. ,.. , _ ._. .... . . _ ,_.. _ . ... --.. --. --. . . .___
added in the volume ratio of 1 : 1, the precipitate of
undigested casein which is ~ormed is filtered off, and the
protein fragments produced during degradation are determined
in the filtrate by any desirable method of determining protein.
By way of example ? the method described by Layne in Methods
f Enzymology, 3 (1957), pages 448 ff., ~ne~r~rat~d hcrcin
... ....
~-:~ is suitable for this purpose.
A blank value~ in which trichloroacetic acid and then
casein solution are added, has to be prepared for each measuring
experiment. In addition to the blank value of the reagents,
this blank value gives the proportion of low molecular peptides
present in the enzyme solution before digestion. In the methods
specified~ the difference between the main value and the blank
value is then compared with the extinction which a specific
! quantity of tyrosine yields in this analysis~ This quantity
of tyrosine is then indicative of the proteolytic activity of
the enzyme present: an enzyme unit (TU) is that quantity of
enzyme which causes the same extinction difference between the
main value and the blank value per ~ln~te as a 1 M tyrosine
solution which is used instead of the enzyme solution.
It is readily possible to measure the proteolytic
activity at pH values above and below 4.5 by suitable adjust-
ment of the casein solution, although it is advantageous to
substitute citric acid for the additive of acetic acid.
In the case of the present invention, the proteoly~ic
activity in the softening liquor should be from about 5 to
100 mTU/liter. This corresponds to from about 0.005 to 0.05
g/l of an enzyme concentrate obtained in accordance with the
data given above.
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. .
, . ,. ,, :
J)~
The special advantage of the enzyme used resides in
its high proteolytic ackivity in a pH range of from about 3.5
to 6.o, preferably from about Ll.5 to 5.2, ~avorable for the
softening of furs, whereby the furs can be softened to an
optimum ex~ent with a relatlvely small dosage without adding
carbohydrases. In particular, the protease is distinguished
by a low content of collegenase-, elastase-, and keratinease
activities, whereby the risk of loss of the hair is consider-
ably reduced compared with former preparations.
In addition, the low content of amidase and exopepti-
dase activities of the enzyme used in the present invention
preparation has a favorable effect on the loosening of the
hair in that the denatured, agglutinating proteins are only
partially hydrolyzed and dissolved out of the skin struckure,
whereby its -original swelling capacity is restored, although,
on the other hand, the regulating effect of these proteins on
the water balance of bhe collagen fibers is not lost.
Furthermore, a fundamental advantage resides in the
fack that khe agents used in the presenk invention develop kheir
optimum e~fect at a working pH value of from about 4.5 ko 5.2,
whereby there is no need to use acid and the risk of acid
swelling is avoided. The alkernative use of non-swelling,
although more expensive, organic acids such as naphthalene
sulfonic acid or oxyisobukyric acid, is also not necessary.
The preferably desired pH range of from about 4.5 ko
5.2 is automatically adjusted when softening with an enzymatic
sof~ening agent when the softening liquor contains a relatively
large amoun~ of sodium bisulphite in addition to ammonium
sulphate. In practice, from about 0.2 to 2 g/l of sodium
bisulphite is used in addition to from about 0.05 to 0.5 g/l
o~ ammonium sulphate, the quantity ratio being from about
2 : 1 to 4 : 1. The enzyme can be combined with the salts
to form an enzymatic softening agent. A mixture of this kind
comprises, for example, from about 65 to 80% of sodium
bisulphite, from about 17 to 35% of ammonium sulphate, and
from about 0.5 to 5% of enzyme. The mixture is used in
quantities of from about 0.5 ~o 5 g/l of softening liauor.
The liquor ratio (hide : softening liquor) is from about 1 : 1~
to 1 : 30, and the liquor temperature is from about 10 to 40C.
The softening action is intensified by the joint use
of an approximately equal quantity of nonionic wetting agent ~-
such as the adduct of 9 mols of ethylene oxide to nonylphenol.
Anionic wetting agents, particularly Na-C12/1g - sulphosuccinate,
are also suitable. Excellent softness and wad-like nature of
the furs is thereby obtained in con~unction w~th the enzyme
used in the present invention, with a more rapid softening
process without the risk of loosening of the hairs.- The
wetting agents are normally used in a quantity of approximately
0.2 to 2 g/l.
To avoid any loss of the hair when treating high-grade
furs, it may be advisable to perform the enzymatic softening
process after a normal wetting agent softening and washing
process in a conventional fur pickle in the presence of
inorganic salts such as common salt and/or ammonium chloride.
Quantities of from abouk 20 to 50 g/l of common salt and from
abouk 2 to 10 g/l of ammonium chloride are normally used in
the pickle. Adjustment to pH values of approximately 2.5 to 3
is effected by, for example, adding formic acid.
E X A M P L E S
.
The present invention can be illustrated by the
following examples and is not to be construed as being limited
thereto.
EXAMPLE 1
.
Dried rabbit-skins were softened with 1 g/l of a
mixture comprising: -
77.4% of sodium bisulphite, anhydrous
21.5% cf ammonium sulphite, anhydrous
1.1% of enzyme
for approximately tw~nky hours at approximately 25C with a
liquor ratio of l : 20. Satisfactorily swollen rabbit-skins
were obtained which can be finished in a conventional manner.
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EXAMPLE 2
Dried rabbit-skins were softened with
1 g/l of the m:Lxture set forth in Example 1, and
1 g/l of nonylphenol -9 E0 (E0 = ethylene oxide)
for approx~mately 15 to 20 hours at 25C with a liquor ratio
of 1 : 20. Satlsfactorily swollen skins were obtained which
can be further processed in a conventional manner. -
EXAMPLE 3
Salted sheep-skins were softened with
0.5 g/l of the mixture set forth in Example 1, and
0.5 g/l of a sulphosuccinate
for approximately fifteen hours at approximately 25C with a
liquor ratio of 1 : 20. The skins, which swelled in a parti-
cularly satisfactory manner and, were further processed in a
conventional manner, a particularly soft, wad-like feel being
produced after tanning.
.
EXAMPLE 4
Air-dried mink pelts were softened in a conventional
manner with a wetting agent softener, washed, and treated for
six hours at 30C with
- 30 g/l of common salt
: 5 g/l of ammonium chloride
~ 1 to 2 g/l of the mixture in accordance with Example 1.
They were subsequently pickled overnight with an addition of
40 g/l of common salt
5 to 8 g/l of 85% formic acid
and finished in a conventional manner. A particularly softened
mink fur was therby obtained, wlthout the risk of loss of the
hair~ -
The preceding specific embodiments are illustrativeof the practice of the invention. It is to be understood,
however, that other expedients known to those skilled in the
art, or disclosed herein, may be employed without departing
from the spirit of the invention or the scope of the appended
claims.
